98 BRITISH INSECTS 



quitoes, the two popular names being synonymous, 

 notwithstanding the current belief that a " mos- 

 quito " is a much more formidable insect than a 

 " gnat." Some of the spotted-winged gnats (or mos- 

 quitoes) of the genus Anopheles which are found in 

 Britain are, in other countries, responsible for the 

 spread of the parasite that causes malarial fever ; but 

 since this disease has disappeared from our islands, 

 the " bite " of these insects is attended by no more 

 serious consequences than temporary local inflamma- 

 tion. The common grey gnat 1 is another trouble- 

 some blood-sucker, but is not, so far as is known, con- 

 cerned in the spread of disease in any part of the 

 world where it occurs. All told, there are about 

 twenty-two species of British gnats, including some 

 that have not been observed to " bite." The larvae 

 are all aquatic, and feed on minute organisms, both 

 animal and vegetable. Those of the genus Culex are 

 the familiar " wrigglers" that are so common in water- 

 butts and cisterns in the summer. Each is furnished 

 with a respiratory tube near the tail-end, and this 

 communicates with the tracheal system. When 

 taking in air the Culex larva suspends itself at an 

 angle from the surface- film, whereas the differently 

 shaped larva of Anopheles lies perfectly horizontal. 

 The pupae float at the surface, and breathe through a 

 pair of trumpet-like tubes on the thorax. 



It should be noted that (with one or two possible 

 exceptions) the blood-sucking habit among flies of the 

 sub-order Orthorrapha is confined to the female sex. 

 The males, if they feed at all, subsist on vegetable 

 juices as, indeed, the females are well able to do if 

 their favourite food is not obtainable. 

 Culex pipiens. 



